Fuse adapter



June 7, 1966 A. R. NORDEN FUSE ADAPTER Filed May 28, 1963 f s. M M

N an m W 1 E W mm ATTORNEYS United States Patent 3,255,329 FUSE ADAPTERAlexander R. Norden, New York, N.Y., assignor to Murray ManufacturingCorporation, Brooklyn, N.Y., a corporation of New York Filed Mar..28,1963, Ser. No. 268,725 2 Claims. (Cl. 200-119) This invention relatesgenerally to fuse adapters for receiving type S fuses. The invention ischaracterized by a novel spacing member which eliminates all possibilityof connecting into an electrical circuit a fuse of higher rating thanthe electrical circuit may safely carry. The invention is useful in anytype S fuse adapter, but it is particularly useful in the type S fuseadapters described incopending patent application Serial No. 291,771,which was filed on July 1, 1963 for a Fuse Mounting Assembly.

Type S fuses are designed to minimize the possibility of connecting intoan electrical circuit a fuse of higher rating; e.g. connecting a 30 amp.fuse into a 20 amp. circuit, thereby allowing the circuit to becomesubstantially overloaded without blowing the fuse. This is done by usingdifferent screw threads on different type S fuse sizes and by usingdifferent dimensions for the line contact of the fuse. Under ordinaryconditions, the different screw threads and different contact dimensionsare adequate to' prevent the fuse from making contact if it is insertedin the wrong size fuse holder. In some cases, however, it is possiblefor the fuse to make contact in the wrong size fuse holdernotwithstanding the difference in screw threads and contact dimensions.

Accordingly, the principal object of this invention is to provide a fuseadapter which eliminates all possibility of connecting into anelectrical circuit a fuse of higher rating than the electrical circuit.

Other objects and advantages of the invention will become apparent tothose skilled in the art from the following description of one specificembodiment of the invention, as illustrated in the attached drawings, inwhich:

FIGURE 1 is an elevation view of a first type S fuse; FIGURE 2 is anelevation view of a second type S fuse;

FIGURE 3 is a plan view of a fuse holder with a type S fuse adapterinserted therein;

FIGURE 4 is an elevation section taken on the line 4-4 of FIGURE 3;

FIGURE 5 is a perspective view of'a portion of the fuse holder shown inFIGURES 3 and 4;

FIGURE 6 is an elevation section of one illustrative embodiment of thisinvention; and

FIGURE 7 is an elevation section of a fuse holder with the fuse adapterof FIGURE 6 inserted therein.

FIGURE 1 shows a prior art type S fuse, which comprises a ceramic bodymember 10 on which are formed rectangular screw threads having anaccurately determined pitch and width. The ceramic body 10 is enlargedat the top to form a shoulder 12, which supports a metallic load springcontact 14. The ceramic body 10 is hollow, and the spring load contact14 is coupled to the inside of body member 10 through a slot formedtherein. A fuse element is connected within the hollow portion of body10 between the load contact 14 and a line contact 16, which is attachedto the bottom of body 10. The top of the body 10 is closed by a metalliccap 18, which contains a mica window to permit visual inspection of thefuse element.

The fuse shown in FIGURE 1 is a amp. fuse. FIG- URE 2 shows a amp. typeS fuse, which differs from the 20 amp. fuse only in the length of theline contacts 16 and 16'. This difference of length, however, iscritical because it ordinarily prevents a 30 amp. fuse from mak-3,255,329 Patented June 7, 1966 ing contact in a fuse holder which isdesigned to receive a 20 amp. fuse. In a 20 amp. fuse holder, the threaddimensionsare selected so that the line contact of the 30 amp. fuse willnot touch the line contact of the fuse holder when the 30 amp. fuse isfully screwed into the socket. The 20 amp. fuse, however, will makecontact in the 20 amp. fuse socket because of its longer line contact.This can be better appreciated by referring to FIGURES 3 and 4, whichshow a fuse holder with a type S fuse adapter inserted therein. (Thisparticular fuse holder and fuse adapter are disclosed and claimed in theabove-noted copending patent application.)

Referring to FIGURES 3 and 4, the holder comprises a block 20 ofinsulating material in which is formed a generally cylindrical recess22. A metallic line contact 24 is located in the bottom of the recess(FIGURE 4), and a metallic load contact 26 is located in one side of therecess. Two rectangular slots (FIGURE 3!) are formed in the sides ofrecess 22 to receive a fuse adapter, which can be a type S fuse adapteror an Edison type fuse adapter, as explained fore fully in theabovenoted copending US. patent application. In this particular example,a type S fuse adapter is shown inserted in the recess of the fuseholder.

The type S fuse adapter comprises a hollow shell member 28 which is madeof insulating material and threaded on the inside to receive a type Sfuse. Shell member 28 is secured on the top to a metallic clip 30, whichis disclosed more fully in FIGURE 5. Clip 30 has two downwardlyprojecting legs 32 and 34 each of which is provided with a correspondinglanced hook member 36 and 38. When the fuse adapter is inserted into thefuse holder recess, hook members 36 and 38 engage in matching notches36' and 38' (FIGURE 4)-to secure the fuse adapter in the recess. Itshould be noted that notch 36 is formed in load contact 26, which meansthat clip 30 acts as an extension of load contact 26. When a 20 amp.fuse (FIGURE 1) is screwed into shell member 28, the load contact 14 ofthe fuse bears against the top of clip 30, thereby connecting fuse loadcontact 14 to holder load contact 26. The line contact 16 of the 20 amp.fuse makes contact directly with the line contact 24 of the holder viaan opening formed in the bottom of shell member 28.

When a 30 amp. type S fuse (FIGURE 2) is screwed into a 20 amp. fuseadapter, however, as indicated by the dashed lines in FIGURE 4, the linecontact 16 of the fuse does not normally touch fuse holder line contact24 because of the difference of length between contacts 16 (FIGURE 1)and 16' (FIGURE 2). Under normal conditions, this prevents the 30 amp.fuse from being connected into a 20 amp. circuit. It should be noted,however, that there is a small gap G (FIGURE 4) between the bottom ofthe fuse adapter and the fuse holder recess. This gap is necessary toinsure that lanced hooks 36 and 38 will snap into their correspondingnotches 36' and 38' when the fuse adapter is inserted into the fuseholder recess. But if the gap G is larger than the difference of lengthbetween the line contact 16 of the 20 amp. fuse and the line contact 16'of the 30 amp. fuse, the 30 amp. fuse will make contact in the 20 amp.socket inspite of the difference of length in the line contacts 16 and16'. Furthermore, since the difference of length is quite small, thelikelihood that this abnormal condition will occur is reasonably high.

In accordance with this invention, there is provided means to insurethat the 30 amp. fuse cannot make contact in a 20 amp. socket when thegap G is larger than the difference of length between theline contactsof the two fuses. This can be better appreciated from an examination ofFIGURES 6 and 7, which show one illustrative embodiment of theinvention.

' notches.

Referring to FIGURE 6, the fuse adapter of this invention is similartothe prior art fuse adapters except for the bottom portion, whichcontains a spacer 40 whose dimensions are selected to positively preventa 30 amp. fuse from making contact in a 20 amp. fuse adapter. The insidediameter D of spacer 40 is selected to be larger than the outsidediameter of the fuse line contact 16 and the holder line contact 24 butsmaller than the inside diameter of fuse body 10. Therefore, when a fuseis screwed into the fuse adapter socket of this invention, as indicatedby the dashed lines in FIGURE 7, the bottom of the fuse body contactsthe top of spacer 40 and the bottom of spacer 44 contacts the bottom ofthe fuse holder recess. The fuse line contact 16 and the holder linecontact 24 extend through the center of spacer 40 and will meet if thelength L of the spacer is shorter than the length of fuse line contact16 plus the height H (FIG- URE 4) of holder line contact 24. Therefore,in accordance with this invention, the length L of spacer 40 is selectedto be shorter than the length of fuse line contact 16 plus height H butlonger than the length of fuse line contact 16' plus height H. Thisallows the 20 amp. fuse to make contact in the fuse adapter butpositively prevents the 30 amp. fuse from making contact. It should benoted that spacer 40 is loosely fitted into the bottom of shell member28 so that it can readily slide up and down to allow the fuse adapter tobe snapped into the fuse holder. In order for lanced hooks 36 and 38 tobe engaged in their corresponding notches 36' and 38, it is necessary tohave a small gap 6' between the bottom of the fuse adapter and the fuseholder so that the lanced hooks can be pushed past their correspondingIf spacer 40 were rigidly attached to the bottom of the fuse adapter, itwould prevent lanced hooks 36 and 38 from being moved past theircorresponding notches, and thus prevent the adapter from being easilysnapped into the fuse holder.

Spacer 40 can be made of any suitable material, either metallic ornonmetallic, but for each of manufacture and assembly, it is preferablymade of brass in the form of a cylinder having a flange at one end only.In this case, the unflanged end of the cylinder is inserted through thehole in shell member 28 from the inside and then peened over to form thelower flange on sleeve member 40. The peening is done over a shim placedagainst the cylinder on the bottom of shell member 38. The shim, ofcourse, is removed after the peening operation has been completed, andthe thickness of the shim will determine the overall length L of thefinished spacer. In general, the thickness of the shim should beselected to be equal to the desired overall spacer length minus thethickness of the spacer flanges and the thickness of the bottom of shellmember 28. The desired overall spacer length depends on the length ofthe line contacts of the fuses and fuse holders, as explained earlier.

From the foregoing description it will be apparent that this inventionprovides a fuse adapter which eliminates all possibility of connectinginto an electrical circuit a fuse of higher rating than the electricalcircuit. It should also be understood that this invention is by no meanslimited to the specific embodiment disclosed herein by way of example,since many modifications can be made in the disclosed structure withoutdeparting from the basic teaching of this invention. For example, thespacer member of this invention does not have to be formed in the shapeof a flanged cylinder; it could be a plain cylinder with holes drilledthrough the top and bottom to receive stop pins, or it could be flangedat one end and drilled to receive a stop pin at the other end. These andmany other modifications of the disclosed structure will be apparent tothose skilled in the art, and this invention includes all modificationsfalling within the scope of the following claims.

I claim:

1. A cup-shaped fuse receiving adapter removably inserted into a fuseholder recess which contains a line contact of predetermined height Habove the bottom of the recess, said adapter including means cooperatingwith said recess for the fixed positioning of said adapter therein, andreqiuring a predetermined initial gap between said adapter and saidrecess; a hollow spacer'member passing through an aperture in the bottomof said adapterand having two open ends for receiving respectively theline contact of said fuse holder and the line contact of a fuse, saidspacer being shorter in axial dimension than the combined height H plusthe length of the line contact of a fuse of predetermined rating andlonger than the corresponding dimension of higher rated fuses, and meanslimiting said spacer to a predetermined longitudinal displacementrelative to said adapter whereby said spacer may effectively perform itsfunction Without obviating the gap necessary for insertion of theadapter into the recess.

2. The combination defined in claim 1 in which said hollow spacer membercomprises flanges at both ends thereof for limiting said spacer memberto said predetermined longitudinal displacement.

References Cited by the Examiner UNITED STATES PATENTS 1,832,194 11/1931Esser 200-119 1,910,482 5/1933 Stoddard 200-119 1,948,421 2/1934 Johnsonet a1. 200-l1'9 1,956,337 4/1934 Wood 2001 19 1,969,257 8/1934 Cowles2001i9 FOREIGN PATENTS 46,456 2/ 1911 Austria.

BERNARD A. GILHEANY, Primary Examiner.

HIRAM B. GILSON, Assistant Examiner.

1. A CUP-SHAPED FUSE RECEIVING ADAPTER REMOVABLY INSERTED INTO A FUSEHOLDER RECESS WHICH CONTAINS A LINE CONTACT OF PREDETERMINED HEIGHT HABOVE THE BOTTOM OF THE RECESS, SAID ADAPTER INCLUDING MEANS COOPERATINGWITH SAID RECESS FOR THE FIXED POSITIONING OF SAID ADAPTER THEREIN, ANDREQUIRING A PREDETERMINED INITIAL GAP BETWEEN SAID ADAPTER AND SAIDRECESS; A HOLLOW SPACER MEMBER PASSING THROUGH AN APERTURE IN THE BOTTOMOF SAID ADAPTER AND HAVING TWO OPEN ENDS FOR RECEIVING RESPECTIVELY THELINE CONTACT OF SAID FUSE HOLDER AND THE LINE CONTACT OF A FUSE, SAIDSPACER BEING SHORTER IN AXIAL DIMENSION THAN THE COMBINED HEIGHT H PLUSTHE LENGTH OF THE LINE CONTACT OF A FUSE OF A PREDETERMINED RATING ANDLONGER THAN THE CORRESPONDING DIMENSION OF HIGHER RATED FUSES, AND MEANSLIMITING SAID SPACER TO A PREDETERMINED LONGITUDINAL DISPLACEMENTRELATIVE TO SAID ADAPTER WHEREBY SAID SPACER MAY EFFECTIVELY PERFORM ITSFUNCTION WITHOUT OBVIATING THE GAP NECESSARY FOR INSERTION OF THEADAPTER INTO THE RECESS.